(a) Field of the Invention
The present invention generally relates to cutting of a substrate, and more particularly to apparatus and method for cutting a brittle object such as a glass substrate for use of an LCD panel using a laser.
(b) Description of the Related Art
Liquid crystal display (LCD) devices are a well known form of flat panel display. Especially, the smaller, lighter and less power consumptive characteristics make the LCD devices considered as one of the most contending display devices to replace the cathode ray tube (CRT).
LCD devices include two pieces of glass substrates, and a liquid crystal inserted between the two glass substrates. The liquid crystal acts as an optical shutter for an incident light by changing its alignment state by applying an electric field, and thereby an image is displayed on the LCD screen.
To enhance a productivity in manufacturing such LCD devices, methods for making a plurality of panels in a single process have been proposed. One method is using a glass substrate having a size corresponding to those of a plurality of unit panels, for example, 6 unit cells.
When a thin film transistor (TFT) LCD is manufactured using two substrates of the above-mentioned large 6 unit LCD panel size, a gate line, a data line, a thin film transistor, a pixel electrode, an alignment film and other components necessary for 6 unit TFT substrates are formed on the inner surface of one of substrates, while a color filter layer, a counter electrode, a black matrix and the like which are necessary for 6 unit color filter substrates are formed on the inner surface of the other.
The two glass substrates are produced as a unit panel after undergoing a process of attaching two glass substrates using a sealant, a cutting process, a liquid injecting process, an end seal process, and a process of attaching a polarizing film.
FIG. 1 is a plan view of a mother glass substrate 1 for cutting, where cutting keys 20 are formed on each corner of LCD unit cells 6, and scribe lines 4a, 4b are defined along the cutting keys 20.
During the cutting process, a preliminary cutting groove having a selected depth is formed along the scribe lines 4a, 4b on the mother glass substrate 1 using a diamond cutter. Then, an impact is added onto the glass substrate 1 so as to separate LCD unit cells 6 from the mother glass substrate 1.
However, a cutting apparatus such as the diamond requires an impact for a complete separation after the preliminary cutting groove is formed, which scatters small glass chips all around the cutting line. Therefore, an additional dust collection device is needed in order to prevent a failure caused by those fine glass chips.
Moreover, a plurality of rough edges as shown in FIGS. 2A and 2B, which are expanded views of portions E1, E2 of FIG. 1, are generated when the mother glass substrate 1 is cut by a diamond cutter. A high stress is concentrated on the rough edges, and a higher stress is concentrated on a portion 8 that is extremely rough. Therefore, when the unit panel 6 is separated by an impact which is added after the preliminary cutting groove is formed, the unit panel 6 is separated along the portion 8 where a high stress is concentrated on, not along the preliminary cutting groove (marked as a dotted line). This failure may cut out an active area.
Such a problem occurs frequently while manufacturing a tiled LCD panel for a large screen display.
FIG. 3 is a plan view of an LCD panel 20 where the four unit panels (A to D) are tiled, and FIG. 4 is an expanded view of the portion E4 shown in FIG. 3.
As shown in FIGS. 3 and 4, assume that the unit panels cut by the diamond cutter are bonded by an optical bond 22. When the two LCD unit glasses A and B having rough cut faces 24 and 25 are bonded, a seam line 22 becomes at least 2 mm wide, due to the prominence and depression margin of cut faces 24 and 25 of LCD unit glass A and B. Therefore, the black matrix at the bonding boundary of the glass A and B also becomes at least 2 mm wide to cover the seam line 22. The black matrix at the bonding boundary is much wider compared with that of the black matrix on the surfaces of the two LCD unit glasses A and B. As a result, the seam line 22 distinguishes itself on a screen of the tiled LCD panel 20 during operation and it appears that the image is divided by the seam line. To prevent this, a minimum seam line width that can be achieved is calculated beforehand. Then, the width between the pixels of the LCD panel is designed to be the same as the calculated minimum width of the seam line, so that the seam line may serve as a black matrix, which prevents the split appearance of screen.
That is, an overall resolution of the tiled LCD module is determined by the width of the seam line. Therefore, to enhance the overall resolution of the tiled LCD module, the width of the seam line 22 needs to be narrowed.
However, narrowing the seam line 22 is extremely difficult to achieve due to the margin of error when cuffing the LCD unit glass by a diamond cutter. Therefore, a large tiled LCD module with a low resolution is used for an outdoor projects which do not require a high resolution, despite of its high cost.
When the glass substrate 1 is cut along the scribe line 4a, i.e., a first cutting line, and is cut along the scribe line 4b, i.e., a second cutting line, the failure as shown in FIGS. 2A and 2B may frequently occur in the cross point where the scribe lines 4a and 4b cross each other.
If the substrate is cut by laser, even a minute crack is not generated at the cut surface. This is more important when the cross point is a panel pad or an active area.
A conventional cutting apparatus using a laser beam has following problems.
Coolant sprayed for cooling down the highly heated glass hinders the laser beam""s cutting force of the glass substrate by dispersing the beam""s radiation.
If gas is employed as coolant, the cooling gas becomes hot while cooling down the glass substrate. Thus, molecule of the gas moves actively, and the cooling gas is diffused into the laser beam output from a focusing lens housing, thereby scattering the laser beam.
If liquid is employed as coolant, the laser beam is also scattered due to vapors generated when the cooling liquid cools down the glass substrate.
If the laser beam is so-scattered, the heated area of the glass substrate becomes wider while the heating temperature becomes low. Thus, the crack may not be generated or may not propagate to inner surface of the glass substrate, which prevents complete cutting of the LCD unit cell from the glass substrate.
Another problem is that the LCD unit cell may be spotted and the liquid crystal injection opening of the LCD unit cell may be blocked when the coolant dries up.
Moreover, the coolant sprayed from the cooling unit is splashed, which causes an impediment of the laser cutting apparatus and scattering of the laser beam.
The aforementioned laser cuffing process of the glass substrate is performed in a dark chamber, and the laser beam at an infrared ray band having approximately a wavelength of 1300 mm. Therefore, a worker cannot see whether the cutting laser beam is proceeding straight along the scribe line.
The crack moves along the direction in which the laser beam proceeds. Therefore, if the cutting laser beam goes out of the scribe line and turns to the inside of the LCD unit cell, the crack is also propagated toward the inside of the LCD unit cell. Thus, if the scanning line of the laser beam cannot be seen by the worker, all the LCD unit cells cut from the glass substrate may fail.
Any failure in the process of cutting one piece of glass substrate may in sequence cause another failure in the process of cutting a number of glass substrates in the subsequent process, which may result failures in a large number of LCD unit cells.
This is because a worker cannot individually confirm the cutting state of the glass substrate coming out of the chamber after finishing the laser cutting step.
Another problem is that, even though a worker recognizes any failure in cutting, a quite long period of time is required for an alignment between the scribe line formed on the glass substrate and the cutting laser beam, which lowers a productivity.
It is therefore an object of the present invention to prevent a cut failure occurring, end, and the cross point of cutting lines, when cutting a glass substrate and a panel.
It is another object of the present invention not to generate glass chips while of cutting a glass substrate and a panel.
It is still another object of the present invention to obtain a smooth cut face of a glass substrate and a panel.
It is further another object of the present invention to prevent a coolant from scattering a laser beam.
It is yet another object of the present invention to prevent the surface of an LCD unit cell or a liquid injecting opening from contaminated or blocked by a coolant.
It is yet another object of the present invention to prevent an impediment of a laser cutter caused by a coolant sprayed for the purpose of cooling down the laser scanned portion.
It is yet another object of the present invention to prevent sequential failures in LCD unit cells by checking a path of the laser beam for cutting a glass substrate so that a worker can easily confirm whether the cutting laser beam deviates from a scribe line.
It is yet another object of the present invention to enhance productivity by correcting the laser beam path when it deviates from the scribed line and aligning the laser beam with the scribe line.
It is yet another object of the present invention to provide a tiled LCD module having a high resolution by minimizing the width of a seam line formed at a boundary surface between the tiled LCD panels.
To accomplish the above objects, according to one aspect of the present invention, a laser cutter includes a laser unit for irradiating a laser beam with a specific wavelength along a cutting line marked on an object being cut; and a cooling unit for cooling the cutting line which said laser beam has been irradiated.
The laser cutter further includes a pre-scriber for forming a pre-cut groove at a selected portion, for example, the start edge, end edge or crossing point of the marked cutting lines before the laser beam is irradiated along the marked cutting line.
According to another aspect of the present invention, a laser cutter further includes a coolant inhaler for inhaling coolant sprayed toward the object being cut from a cooling unit. The cooling unit includes a coolant supplying part and a spraying nozzle. The coolant inhaler is disposed at the back of the cooling unit such that the sprayed coolant is effectively inhaled. The coolant inhaler includes an inhaling pipe disposed at the back of the cooling unit with respect to the traveling direction of the laser unit and a pump to vacuum the inhaling pipe.
According to still another aspect of the present invention, a laser cutter includes a light modulator that perceives traveling paths of a first laser beam by modulating a part of the first laser beam into a second laser beam having another wavelength and transmits the remainder of the first laser beam.
The light modulator comprises a beam splitter for splitting an incident laser beam of a laser unit into two laser beams by transmitting a part of the incident laser beam and reflecting the remainder of the incident laser beam, a light modulation part for modulating the laser beam reflected from the beam splitter into a visible ray thereby to generate an indicative laser beam, and a reflective mirror for reflecting the modulated indicative laser beam at a selected angle.
The cutting laser beam transmitted and the indicative laser beam reflected are both irradiated on the marked cutting line such that the indicative laser beam is positioned behind the cutting laser beam with respect to the traveling path of the two beams.
According to further another aspect, a laser cutter includes a first laser unit for irradiating a first laser beam with a first wavelength along a cutting line marked on an object being cut, a cooling unit for cooling the marked cutting line irradiated by the first laser beam to generate cracks at the cooled cutting line, a second laser unit for irradiating a second laser beam with a second wavelength onto the crack of the object being cut, a light detecting part for detecting the second laser beam reflected by the crack; and a control unit for outputting a signal for correcting a path of the first laser beam by comparing a real cutting path obtained by the light detecting part with the marked cutting line to determine whether the real cutting path deviates from said marked cutting line.
Here, the first and second laser units respectively includes a laser oscillating unit for oscillating a laser beam, a refraction lens disposed in front of the laser oscillating unitto refract the laser beam at a selected direction, a focusing lens group for focusing the refracted laser beam on the marked cutting line and a focusing lens housing containing the focusing lens group.
In addition, the light detecting part is a light detecting sensor for detecting light amount of the second laser unit reflected by the crack.
Preferably, in the above-mentioned laser cutters, the cooling unit includes a spray nozzle for spraying coolant, in which the spraying nozzle has an oblique tip. Since the diameter of the laser beam is smaller than that of the spraying nozzle, the most acute portion of the tip of the spray nozzle is aligned with the marked cutting line such that the crack does not deviate from the marked cutting line.
According to yet another aspect, there is provided a method for cutting a brittle object using a laser cutter. The method first detects a cutting line marked on the object and the beginning point of the cutting line. Afterwards, a pre-cut groove of a selected length and depth is formed at the starting edge of the marked cutting line. A laser beam is then irradiated along the marked cutting line, starting from the pre-cut groove. Thereafter, the marked cutting line is rapidly cooled.
The cutting method according to the present invention can be applied to an object having at least two cutting lines normal to each other or arranged at a selected angle. At the cross point of the cutting lines, the pre-cut groove may be formed before the irradiation of the laser beam or when the cross point appears. Here, the pre-cut groove has a selected length along the cutting lines, or may have a circular structure.
Also, the object can be cut by two steps through controlling the cutting depth of the object in each step. The two step cutting substantially prevents the cutting failure due to an irregular crack generated at the rear surface of the object.
According to yet another aspect of the invention, there is provided a method for cutting a brittle object using a laser cutter. The method first irradiates a laser beam along a marked cutting line. Afterwards, the marked cutting line is rapidly cooled. Thereafter, a real cuffing line is perceived by crack generated during the cooling step. Next, it is determined whether the real cutting line deviates from the marked cutting line by comparing the real cutting line with the marked cutting line. If a deviation exists in, the traveling path of the laser beam is corrected.
Here, the real cutting line is perceived by irradiating the laser for the alignment and then detecting light amount reflected by the crack, and the marked cutting line is inputted beforehand.
The above-mentioned laser cutter and cutting method are especially good for the fabrication of a tiled LCD panel.